The present invention relates to a high-frequency inverter for fluorescent lamps, or, more particularly to a fluorescent lamp operating device which improves the lighting on-off cycle life of fluorescent lamps significantly and is suitable for being equipped with a dimming function at the same time.
There have been made available various conventional fluorescent lamp operating devices which have a function equivalent to that of an operating device used for turning on a fluorescent lamp after preheating such as a fluorescent lamp of glow starting type. With respect to one of them, the operating device disclosed in Japanese Patent Laid-Open Publication (JP-A) No. 59-132594 comprises means for turning off the device after a predetermined preheating time at the time of starting by use of a saturable reactor.
In this type of operating device, however, there is no preheating and only the filament is heated with a lamp current after the lamp has been turned on. Therefore, in applications requiring free control of the lamp load, the filament temperature of the fluorescent lamp decreases with the decrease of the lamp current, thereby shortening the lamp on-off cycle life. Another disadvantage of this type of operating device is a high cost due to the combination of a saturable reactor and a capacitor.
A dimming circuit which is separately required for providing a dimming function renders the cost even higher and reduces the reliability.